In a packaging machine there is the need for a conveying system suitable for transferring items and/or containers between sections of the machine itself.
For example, a packaging machine typically comprises a container forming section for picking up and forming containers, a loading section for loading items into containers, a closing section for closing the containers, an output section for expulsion from the machine. The conveying system carries the containers from the container forming section to the loading section, transfers the loaded containers from the loading section to the closing section, and carries the closed boxes to the output section.
A simple and still used conveying system is represented by conveyor belts, which however are poorly flexible because all objects on a conveyor belt move at the same speed maintaining the same distance apart. An evolution of conveyor belts is described in EP 0695703 and is also known as servotrain system or multi-axis system, and essentially comprises several adjacent belts with independent motors and control. A further and more recent evolution of the conveying system is represented by the magnetic drive conveyor and relative movers.
Said conveyor comprises a plurality of movers, sliding along a path. The path is represented for example by a closed-loop track and is formed by joining different straight and curved sections.
The movement of the movers along the path is controlled electromagnetically. Each mover comprises at least one reactive element to interact electromagnetically with active elements incorporated in at least part of the path. The interaction between said active and reactive elements propels the movers and provides the desired control of movement. The active elements integrated in the conveyor are normally represented by windings capable of generating a magnetic field when excited by an electric current, and the reactive elements installed on the movers are represented by permanent magnets.
The movement of each one of the single movers (position, speed and acceleration) can be controlled independently relative the other movers. A magnetic drive conveyor generally comprises also one or more sensors to detect the position of the movers along the path.
The magnetic drive conveyor is known and is described for example in WO 03/105324. A detailed description of the propulsion system is given for example in EP 2 779 390.
A magnetic drive conveyor of the type described above offers several advantages over conventional conveyors: independent control of any number of movers along the same path; possible implementation of complex laws of motion, unattainable with the conventional method; movers propelled with no direct contact and no mechanical parts like belts or gears; low friction; fast speed and acceleration of the movers; accurate control of their position along the path.
The application of magnetic drive conveyors in the field of packaging machines is known in itself. The movers can be used, for example, to carry items or containers, either full or empty, also by means of auxiliary conveying members such as pockets or equivalent means suitably fixed to the movers.
However, up to now the success of said magnetic drive conveyors in the field of packaging machines has been less than expected.
One of the main reasons why embodiments of the prior art are unsatisfactory lies in the interface of the control of the magnetic drive conveyor with the control of the packaging machine itself.
Generally, a magnetic drive conveyor has its own programmable control system that dynamically manages the various movers (motion control) according to a predetermined operating cycle. Said control system is user-configurable to implement a desired law of motion of the movers. Up to now, the prior art has followed the approach of defining a substantially fixed (i.e. static) law of motion of the movers and operating cycle, based on the operations carried out by the packaging machine. For example, in a machine which operates intermittently it is generally chosen to provide intermittent motion of the movers during the operative steps (typically during loading), whereas in other work steps (typically in a return stroke) the motion of the movers can be continuous. Moreover, the flexibility of control of the conveyor is used to make the movers proceed with different speeds along different portions of the path, for example accelerating during the return stroke to reduce the waiting times.
However, this approach only partially exploits the advantages of flexibility and configurability of the magnetic drive conveyor. Following this approach of the prior art, it has been seen that performance is not much better compared to a multi-axis system, and may not compensate for the extra cost of the magnetic drive conveyor. One or more embodiments of the invention aim to solve this problem.